Modular and Efficient Wireless Power Transfer Systems

ABSTRACT

A device has a plurality of coils arranged along a perimeter within the device, where each coil has a winding configured to be coupled to a power converter through a resonant capacitor, and forms a resonator with the resonant capacitor. The device has also a connection core which is magnetically coupled to the plurality of coils. Furthermore, the device has a plurality of power converters, where each power converter is coupled to one of the plurality of coils, and is configured such that a current flowing through the winding of the coil has the same frequency as other winding currents in the device, and the phase angle of the current is approximately equal to the space angle of the coil, so a rotating magnetic field is formed in a space around the device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related and claims priority to U.S. ProvisionalApplication No. 62/559,592, filed on Sep. 17, 2019, entitled “Modularand Efficient Wireless Power Transfer Systems”, which is hereinincorporated by reference.

TECHNICAL FIELD

The present invention relates to power conversion and power electronicsdevices and systems, and, in particular embodiments, to high efficiencywireless power transfer systems.

BACKGROUND

Wireless power transfer (WPT) is desirable for many applications due tobetter customer experience and better tolerance of harsh environment.Although the basic theory of WPT has been known for many years, and WPTtechnologies have been used in some applications in recent years, it hasbeen a challenge to achieve high efficiency wireless power transfer atlow cost. Also, the EMI and noise from a WPT system can causeinterference to electronic devices, and may present hazards to peopleand other animals in the close environment, which are significantconcerns when the power of the WPT system is high.

Therefore, improvements are needed to design a wireless charging systemwith good performance. The goals include accomplishing high power WPTsystems with high efficiency, low magnetic emission, and low cost.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by preferred embodiments ofthe present invention which provides an improved WPT system based onadvanced resonant power conversion.

According to one embodiment of this disclosure, a device has a pluralityof coils arranged along a perimeter within the device, where each coilhas a winding configured to be coupled to a power converter through aresonant capacitor, and forms a resonator with the resonant capacitor.The device has also a connection core which is magnetically coupled tothe plurality of coils. Furthermore, the device has a plurality of powerconverters, where each power converter is coupled to one of theplurality of coils, and is configured such that a current flowingthrough the winding of the coil has the same frequency as other windingcurrents in the device, and the phase angle of the current isapproximately equal to the space angle of the coil, so a rotatingmagnetic field is formed in a space around the device.

According to another embodiment of this disclosure, a system includes aninput port having an input voltage, a first power converter coupled tothe input port and having a first switch network with a plurality offirst power switches, an output port having an output voltage and anoutput current, and a second power converter coupled to the output portand having a second switch network with a plurality of second powerdevices. The system also includes a resonator block comprising aplurality of resonators in which each resonator has a resonantcapacitor, and a first resonator of the plurality of resonators iscoupled to the first power converter, and a second resonator of theplurality of resonators is coupled to the second power converter. Thesystem further includes a connection block having a switching device andcoupled to the first resonator, and the connection block, the firstresonator and the second resonator are configured such that the systemoperates in a wireless charging mode with the resonator block activatedor a wired charging mode with the connection block activated.

According to yet another embodiment of this disclosure, a methodconsists of configuring an output port of a wireless power transfersystem having an output voltage and output current, and providing aplurality of first resonators, where each first resonator has a firstresonant capacitor and a first coil. The first coils are placed along afirst perimeter, and through the first resonant capacitors the firstcoils are connected to a plurality of first power converters having aplurality of first power switches. The method also includes providing aplurality of second resonators, where each second resonator comprises asecond resonant capacitor and a second coil. The second coils are placedalong a second perimeter, and through the second resonant capacitors thesecond coils are coupled to a plurality of second power convertershaving a plurality of second power switches. The method further includesestablishing a magnetic coupling between the first coils and the secondcoils, and configuring a control block to control the system such that arotating magnetic field is established between the first coils andsecond coils in a mode of operation.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures or processes for carrying outthe same purposes of the present invention. It should also be realizedby those skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a block diagram of a resonant power system;

FIG. 2 illustrates a block diagram of a WPT system;

FIG. 3 illustrates a block diagram of a modular WPT system in accordancewith various embodiments of the present disclosure;

FIG. 4A illustrates a schematic diagram of a WPT transmitter inaccordance with various embodiments of the present disclosure;

FIG. 4B illustrates a schematic diagram of another WPT transmitter inaccordance with various embodiments of the present disclosure;

FIG. 5 illustrates a schematic diagram of a WPT receiver in accordancewith various embodiments of the present disclosure;

FIG. 6 illustrates a block diagram of a combined WPT system and wiredcharging system in accordance with various embodiments of the presentdisclosure;

FIG. 7 illustrates a switchable capacitor in accordance with variousembodiments of the present disclosure;

FIG. 8A illustrates a coil assembly for a WPT system in accordance withvarious embodiments of the present disclosure;

FIG. 8B illustrates a coil assembly for a WPT system in accordance withvarious embodiments of the present disclosure;

FIG. 8C illustrates a coil assembly for a WPT system in accordance withvarious embodiments of the present disclosure;

FIG. 8D illustrates a coil assembly for a WPT system in accordance withvarious embodiments of the present disclosure;

FIG. 9A illustrates a side view of a coil assembly for a WPT system inaccordance with various embodiments of the present disclosure;

FIG. 9B illustrates a side view of a coil assembly for a WPT system inaccordance with various embodiments of the present disclosure;

FIG. 10A illustrates an arrangement of multiple windings for a WPTsystem in accordance with various embodiments of the present disclosure;

FIG. 10B illustrates a coil assembly for a WPT system in accordance withvarious embodiments of the present disclosure;

FIG. 11 illustrates an arrangement of multiple windings for a WPT systemin accordance with various embodiments of the present disclosure;

FIG. 12A illustrates a cross section view of a winding in accordancewith various embodiments of the present disclosure;

FIG. 12B illustrates a cross section view of a winding in accordancewith various embodiments of the present disclosure;

FIG. 13 illustrates a system with a WPT transmitter coil assembly and aWPT receiver coil assembly in accordance with various embodiments of thepresent disclosure;

FIG. 14A illustrates a top view of a coil assembly with a shield ring inaccordance with various embodiments of the present disclosure;

FIG. 14B illustrates a top view of a coil assembly with shields inaccordance with various embodiments of the present disclosure;

FIG. 15A illustrates a block diagram of a modular transmitter inaccordance with various embodiments of the present disclosure;

FIG. 15B illustrates a block diagram of another modular transmitter inaccordance with various embodiments of the present disclosure;

FIG. 16 illustrates a block diagram of a modular receiver in accordancewith various embodiments of the present disclosure;

FIG. 17 illustrates a control block diagram of a WPT system inaccordance with various embodiments of the present disclosure;

FIG. 18 illustrates another a control block diagram of a WPT system inaccordance with various embodiments of the present disclosure;

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the variousembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to preferredembodiments in a specific context, namely in high power WPT systems. Theinvention may also be applied, however, to a variety of other systems,including integrated circuits, power converters, power supplies, lowpower wireless power systems, any combinations thereof and/or the like.Hereinafter, various embodiments will be explained in detail withreference to the accompanying drawings.

Power efficiency, electromagnetic emission, system reliability andsystem cost have been critical factors impacting the design and adoptionof WPT technologies. This application discloses several innovativetechniques that can provide significant improvement in these aspects,and uses the battery charging of electric vehicles (EVs) as an examplewhen applicable. For such a high power system, usually a wired chargingsystem is collocated with a WPT system, and the power source may be acpower from a grid system, or dc power from a source such as solar panelsor batteries, but ac input will be used mostly as an example. FIG. 1shows a resonant power system 100 usually used in wired chargingsystems. A power conditioning block 102, usually a power factorcorrection (PFC) converter or other types of ac-dc converters, is usedto convert ac power at the input (Vin) to a dc voltage Vdc, which isthen converted to a high frequency ac voltage waveform through a highfrequency (HF) inverter 104. The high-frequency voltage is then fed to aprimary resonant tank comprising a resonant capacitor C1 and a resonantinductor network comprising a primary winding 107 of a power transformerT1. A secondary winding 108 of T1 is coupled to a rectifier 109, whichconverts the ac voltage across T1 to a dc output voltage Vo, which canbe applied to various load circuits, such as batteries or down-streampower converters. The power control, sometimes to regulated outputvoltage Vo and sometimes to regulate output current supplied to the loadcircuit, is usually implemented as a frequency control of the HF powerinverter 104. Duty cycle control of the HF inverter may also be used ifneeded. Through proper selection of capacitance of C1 and resonantinductance including the leakage inductance of T1, the power switches inthe HF inverter can usually operate under a soft-switching condition,such as zero-voltage switching.

FIG. 2 shows a typical WPT system 200 with magnetic resonance (MR)technology, which includes a power transmitter (TX) 201 and a powerreceiver (RX) 211. Similar to FIG. 1, a PFC converter 202 is used toconvert ac power at the input to a dc voltage Vdc, which is thenconverted to a high frequency ac voltage waveform. In conventional MRtechnology, the resonant coupling link has no power control capability,so the high-frequency ac voltage is generated through two stages: thefirst stage is a dc-dc converter 204 which converts the dc link voltageVdc to another suitable dc voltage 206 to control the power at theoutput of the RX 211, and the second stage is a power amplifier 207which converts the dc voltage 206 to a high-frequency ac waveform,usually at a fixed duty cycle (typically 50% in a half-bridge orfull-bridge topology). The high-frequency voltage is then fed to a TXresonator 208 comprising usually a resonant capacitor and a transmittercoil, and optionally a filter or impedance circuit may be used to reducethe harmonic contents of or intentionally add some harmonic contents tothe current in the transmitter coil. These circuits form a powertransmitter 201. The power receiver 211 comprises a RX resonator 208(usually consisting of a RX resonant capacitor and a RX coil) and a RXpower conditioning circuit 210 (usually a rectifier). When the RX coilis put in the proximity of the TX coil (i.e. in the charging area), amagnetic coupling is established between these coils, and energy can betransferred between them. The power condition circuit 210 can convertthe ac voltage in the RX resonator to a voltage suitable for the loadcircuit, usually a dc output voltage Vo across an output capacity Co.The output voltage can be applied to various load circuits, includingbatteries or down-stream power converters. When the RX is placed nearbythe TX, the RX coil becomes magnetically coupled to the TX coil, and canpick up energy from the TX coil. The power control, sometimes toregulate output voltage Vo and sometimes to regulate output currentsupplied to the load circuit, is usually implemented as a voltagecontrol to the dc voltage 206 of the dc-dc converter in the TX. As theTX and the RX are physically different units, to implement the powercontrol a communication channel between the TX and the RX needs to beprovided. Sometimes this communication is through an in-bandcommunication which modulates a frequency or load in the RX or TX.Sometimes this communication is through an out-band communication suchas a Bluetooth or NFC (near-field communication) channel.

For high power WPT applications, it is usually more desirable to use amodular design approach. It is also more economical to share as manycircuits as possible between the wired charging system and the wirelesscharging system. Also, in a modular design it is desirable to improvesystem performance by further arranging the power converters, the TXcoils, and/or RX coils into modules, and coordinating the operationbetween multi modules. The following discussion presents innovativetechniques that enhance various aspects of system performance.

FIG. 3 shows a modular WPT system which is compatible to and can beintegrated with a wired charging system. The power architecture issimilar to the one shown in FIG. 2, except that a plurality of powerbuses are added. The input 301 of all input power modules 302 may befrom a common source, or several separate sources (labeled as Vin1 toVinM in FIG. 3). The outputs of M input converters 302 can be coupledtogether to form a dc link bus Vdc 303, so the power of these PFCconverter can be added together. If desired ORing and/or current-sharefunctions can be implemented in the input converters. The switchingfrequencies of these input converters may be synchronized withsymmetrical phase shifts between them, so the noise in the modules andthe current ripple of the capacitors on the dc bus can be minimized. Inlight load, some of the input modules may be shut down, so the totalpower losses can be reduced. Also, the input converters can be designedand controlled with redundancy, so if some of them fail the system cancontinue to operate, resulting in significantly improved systemreliability. N transmitter modules 304, each may comprise a TX converter305 and a TX resonator 306, are connected to the dc link bus 303, andare configured to generate a magnetic field to be magnetically coupledto receiver modules 307. The transmitter modules should be controlledsuch that the magnetic field generated by these modules are more or lesssmooth and even in the charging area, so RX modules may work with highefficiency regardless the positions of the RX modules in the chargingarea. In FIG. 3, L RX modules 307, each consisting of a RX resonator 308and a RX power conditioner (usually a rectifier) 309, are shown. Theoutput of L RX rectifiers 307 in L receivers are coupled together toform an output bus Vo. In some embodiments, some receiver modules maygenerate different output voltages if a system has such multi-outputneed. If the TX coils are configured to form a unified magnetic field,the number of transmitter modules/coils may be different from the numberof receiver modules/coils. That is, K, L and N may be equal ordifferent. This gives the system designer more flexibility to optimizethe system design, and to make a system to be adaptable to differentreceivers which may have different power levels and other requirements.

The TX converter 305 may be a single stage inverter such as half-bridge,full-bridge or push-pull inverter as is well known in the industry, orit may be a combination of a dc-dc converter to regulate a voltage atits output and an inverter coupled to the output of the dc-dc converter.The inverters may be controlled with 50% duty cycle, and the switchingfrequencies of all inverters may be synchronized with symmetrical phaseshifts between them. The TX coils of the power transmitters may bemagnetically coupled together and form a TX coil assembly. Similarly,the RX coils of the power receivers may be magnetically coupled togetherand form a RX coil assembly. The power control may be accomplishedthrough a communication channel between the TX and the RX. The powercontrol can be implemented as a central controller at the system level,i.e. use a single power control block 310 to control all TX converters.Alternatively the power control may also be implemented as a distributedcontrol configuration, in which a power control block 310 may controlpart of or even just one of the TX modules 304, and there are multiplepower control blocks in the system with one or multiple communicationchannels between the RX side and the TX side. Sometimes thecommunication between the RX side and the TX side is through an in-bandcommunication through modulating a frequency or load in the RX or TX.Sometimes this communication is through an out-band communication suchas a Bluetooth, WiFi or NFC (near-field communication). The powercontrol can also be split between the TX side and the RX side of thesystem. For example, the output voltage/current/power can be controlledin the RX side, through resonance modulation of changing the resonantfrequency of the RX resonators, or through controlling a dc-dc powerconverter incorporated in the RX rectifiers. The reactive power, whichis directly related to the soft-switching of the power switches in theTX converters, can be controlled in the transmitter side, throughresonance modulation or capacitor switching in the TX resonators orcurrent and voltage control. The communication channel between the RXside and TX side can be used to coordinate the control actions in the TXside and RX side to optimize system performance such as systemefficiency improvement.

In light load, some of the TX modules (TX1 through TXN) or RX modules(RX1 through RXL) may be disabled or shutdown, so the total power lossescan be reduced. Also, the RX modules RX1 through RXK can be controlledwith redundant function, so if some of them fail or not in a goodposition to transfer power efficiently, the system can continue tooperate with the remaining modules, so the system performance andreliability are significantly improved. A current sharing function mayalso be implemented among the TX modules and/or RX modules. At each ofinput stage, transmitter stage and receiver stage, the power control maybe implemented at the module level, treating the system as multiplemodules in parallel, or may be implemented centrally treating the wholesystem as one multi-phase system, as discussed earlier.

Many of the circuits and control algorithms may be shared between awired charging system to save total system cost. For example, all theinput converters, TX converters, and maybe the RX rectifiers may beshared with a collocated wired charging system. All or part of theresonant capacitors, as well as the power transformers may also beshared between a wireless power transfer system and a collocated wiredcharging (or power) system.

FIG. 4A shows an example of component sharing in a transmitter circuit400. Power switches S1 through S4 forms a full-bridge transmitterconverter 402 which is coupled to a dc voltage Vdc at the input 401, andproduces a high frequency voltage at the output port across point a andpoint b. Of course, other types of topologies, such as half-bridge,multi-level, push-pull and hybrid converters can also be used. C1 andCx1 form a resonant capacitor 406, and together with transmitter coil Ltform a transmitter resonator 403, where C1 and/or Cx1 (or part of them)may be a resonant capacitor used also in wired charging system in aresonant topology such as LLC power converter. C1 may not be part ofwired charging system, or even may not be present in an actual design.Cx1 may be additional capacitor switched in when the system is switchedto work in wireless power transfer mode, or in case C1 is not presentthe whole transmitter resonant capacitor. Cx1 may be a variablecapacitor whose capacitance can change over a wide range relativelysmoothly, or a switchable capacitor whose capacitance has a limitedrange of values with bigger steps selectable by the control, so that theresonsystemant frequency of the resonator may be selected or changedover a certain range in view of possible inductance change in Lt. Anexample implementation of a switchable capacitor will be shown in FIG. 7and described later. The voltage across L1 may be used as a shared port405 to be coupled to a wired charging system. Alternative, the outputvoltage from the TX converter (across points a and b in the switchbridge) may be used as a shared port 405 and coupled to a wired chargingsystem. That is, the TX converter and circuit before it, and optionallythe resonant capacitor 606, may be shared between the wireless chargingsystem and the wired charging system, and such circuits can be locatedinside the wireless charging system, or the wired charging system, or asa separate subsystem shared by both.

FIG. 4B shows another example of sharing components in a transmitter400. Here a power transformer T1 and a capacitor C1 are added comparedto the transmitter 400 shown in FIG. 4A. Since the leakage inductance ofT1 is usually designed to be much lower than the inductance of TXresonant coil Lt, the circuit operation is not changed significantlyfrom the transmitter 400 discussed above, except that T1 scales thevoltage up and down with a turns ratio, and the leakage inductance of T1becomes part of the resonant inductance of the resonant tank. Thisscaling can bring the voltage rating of a resonant capacitor Cx1 and anycontrol switches inside it to reasonable values to allow betterselection of components, and also meet safety requirements more easily.C1 and Cx1 are in series and together function as a resonant capacitor.C1 may be a resonant capacitor when its capacitance value is relativelysmall, or may just perform a dc-blocking function when its capacitancevalue is very big, for example three times bigger than that of Cx1. Cx1and/or C1 may be implemented as switchable or variable capacitors. Now awired charging system may be coupled to the WPT system across a primarywinding 404 or a secondary winding 409 of T1, across Lt, or across theoutput voltage of the switch bridge. That is, the TX converter andcircuit before it, and optionally C1, T1 and/or CX1 may be sharedbetween the wireless charging (wireless power transfer) system and thewired charging system, and such circuits can be located inside thewireless charging system, or the wired charging system, or as a separatesubsystem shared by both.

FIG. 5 shows a way in which wireless charging and wired charging mayshare a RX rectifier. Here the resonant capacitor in the RX resonator isoptionally split into two capacitors Crt and Crb, which may be replacedby a single capacitor if needed. Again Crb and/or Crt may be implementedas a switchable or variable capacitor. The receiver coil Lr and resonantcapacitors Crt/Crb form a receiver (RX) resonator 502. When the receiver500 is in a charging zone of a transmitter, it is exposed to themagnetic field generated by the transmitter coils, and energy can betransferred between the receiver and the transmitter. The receiverresonator can be designed to optimize such energy transfer in practicalapplications. The receiver conditioning circuit 506 is shown as afull-bridge rectifier comprising diodes D1 through D4. The circuit 506converts the energy received from Lr to a form suitable for the load.When it is implemented as a rectifier, it produces a stable dc voltageVo at the output port 508. As is well known in the industry, otherswitching devices such as MOSFETs and IGBTs can be used in a rectifieras synchronous rectifier devices, or other circuit types such ashalf-bridge rectifiers, ac-ac converters, dc-dc converters or anycombination thereof may be used to produce an output most suitable forthe load. The wireless charging system may be coupled to a wiredcharging system at input port 505 of the RX conditioning circuit 506 oracross Lr, so that t

The RX conditioning circuit and circuits following it, and optionallythe receiver resonant capacitors may be shared between the wirelesscharging system and the wired charging system, and such circuits can belocated inside the wireless charging system, or the wired chargingsystem, or as a separate subsystem shared by both.

FIG. 6 shows a block diagram of a charging system 600 integrated both aWPT system (wireless charging) and wired charging, by incorporating thetransmitter 400 in FIG. 4B and the receiver 500 in FIG. 5. On the inputside other circuits such as PFC converters were omitted for the sake ofbrevity. The charger system 600 can function as both a wireless chargerand a wired charger, and most components are shared between them. Thereis a WPT resonators block 602 which consists of a TX resonator 403 andoptionally a RX resonator 502. There is also a wired charging connectionblock 604. Usually, only one subsystem, either the wireless charger orthe wired charger is actively operating at a time. There may be switchesin blocks 602 and 604 to disable one or both of these blocks when it isnot in operation. Alternatively, a variable or switchable capacitor mayperform the function of a switch since its capacitance can be set todifferent values to create different impedances: a very low value tocreate a high impedance which prevents significant current to flowthrough, or a very high value to create a low impedance circuit whichallows significant current to flow through. For example, in FIG. 6 Cw1may be set to the lowest possible value when the system is working inWPT mode, and the resonant capacitor CX1 and/or Crr may be set to thelowest possible value when the system is working in wired charging mode.Alternatively, a resonant capacitor in a resonator, such as CX1 or Crr,may be set to the highest value so the resonator exhibits a highimpedance to disable or reduce the power transfer capability of theresonator when such power transfer is not needed. In other embodiments,in wired charging mode, the capacitance of a resonant capacitor (such asCX1 and/or Crr) may be set to a value so a resonator in the WPT path canimprove the performance of the wired charging system, such as to helpcontrol a voltage or current at the output.

A switchable capacitor is configured as a network of capacitors andswitches organized in a few branches, and FIG. 7 shows an exampleimplementation. Different from a variable capacitor whose capacitanceneeds to change in a relatively large range smoothly (i.e. with a finestep, for example the step is less than 1% of its full value)), aswitchable capacitor may have only a few branches so its capacitance canbe switched between a limited set of capacitance (for example no greaterthan 16 values) in a relatively big steps. To reduce the voltage ratingof each capacitor and/or switch, the switchable capacitor may beconfigured as multiple capacitors in series. In FIG. 7, Ct is the topcapacitor, which can be a normal capacitor or also a switchablecapacitor network. The bottom capacitor is shown as a switchablecapacitor network 705. Cbo, which is optional, is in parallel with a fewswitch-capacitor branches, with 3 branches shown in the figure as anexample. There are 8 different combinations of the control switches Sx1through Sx3, considering each of these switches may be in ON or OFFstate. The switchable capacitance can have a different equivalentcapacitance under each of these combinations. This allows thecapacitance of a resonant capacitor be changed according to controlsignals of the switches. When a higher number of switch-capacitorbranches are used, and when the capacitance of the switchable capacitorsin these branches can be arranged in a doubling relation (i.e. thecapacitance of a capacitor is approximately twice the value of the onein an adjacent branch), the equivalent capacitance of the switchablecapacitor can change over a wide range with approximately even and finesteps, so the switchable capacitor becomes a variable capacitor. Ct doesnot need to be physically connected to the bottom capacitor directly.For example, in FIG. 4A Ct may be moved to the other side of L1 withoutimpacting the basic operation of the system. Such a more symmetricalarrangement can reduce the EMI of the system.

Switching means may be used to configure the system so only onesubsystem is active at a time. For example, if the system is intended towork in wired charging mode then components and subsystems dedicated towireless charging (for example L1 in FIG. 4A or L1 and Cx1 in FIG. 4B)are not activated. Similarly switching means may be used so in wirelesscharging mode the components and subsystems dedicated to wired chargingsystem are not activated. Please note a resonant tank or a coil of aresonator may be de-activated by not switching the switches in the powerconverter coupled to it, or by making the resonant capacitance verysmall or very big so the operation of the resonant tank is far away fromits resonant state and presents a high impedance. This may be achievedby controlling a switchable or variable capacitor.

In a modular design, multiple TX coils may be integrated into one TXmagnetic structure such as a TX coil assembly, and the TX coils in amagnetic structure may be magnetically coupled together. Similarlymultiple RX coils may be integrated into one magnetic structure such asa RX coil assembly. The magnetic coupling between the coils may be usedto strengthen the magnetic field in a space close to a coil assembly. Bycarefully designing and locating the coils and controlling the currentsin the coils, a smooth and strong magnetic field can be formed near thetransmitter magnetic structure to provide a good charging space orcharging area for intended RX coils, but outside the charging space thestrength of the magnetic field may be significantly reduced to reduceEMI emission and noise while reducing system cost, size and weight. Inthis way, a good magnetic coupling can be maintained between the RXcoils and TX coils even when there is a misalignment between the RXmagnetic structure and the TX magnetic structure. One way to achievethis is to generate a rotating or traveling magnetic field in thecharging space, which is similar to the rotating or traveling magneticfield in a poly-phase electric machine. FIGS. 8A to 8D (collectivelyFIG. 8) show examples of multiple coil arrangements in a magneticstructure, which may be a TX or RX coil assembly. The big arrow signs inFIG. 8 illustrate the direction of the rotating magnetic field. Ofcourse, the magnetic field can also be configured to rotate in theopposite direction of the big arrows. FIGS. 9A and 9B (collectively FIG.9) show some cross-section views which highlight the details of coils.

In the example of FIG. 8A, the coil assembly 800 consists of 4 coilslabeled as Coil L1 through Coil L4, each consisting of a winding 801around a magnetic winding core 802. Please note that the winding core802 is optional, i.e. a coil may be an air-core coil. These coils may bearranged in a symmetrical and usual co-planar fashion in the magneticstructure, and are magnetically coupled by a connection core 806, whichmay be a plate or a plurality of plates made of magnetic materials suchas ferrite, iron power, silicon steel, MPP materials, or magnetic films.Sometimes the connection core is also called a magnetic shield. Aroundthe center of the magnetic structure, there may be one or more centercores Co 803, and some center cores may have windings around them in asimilar way as in the 4 coils around the outside perimeter. These coilsmay be arranged in a symmetrical way as in a poly-phase electricalmachine, and can generate a rotating or traveling magnetic field in thespace above them when currents with the correct phase displacementflowing through them. The area or space where the rotating magneticfield is relatively strong can be used as a charging area or chargingspace. The winding cores, connection core and center cores can be madefrom ferrite, silicon steel or other suitable magnetic material. As isshown in FIG. 9A, there may be air gaps arranged between two cores, sothat the magnetic coupling between coils may be adjusted by the lengthof the air gaps. The air gaps can also be arranged to separate themagnetic structure into several pieces such as bars or plates tosimplify the manufacturing process and/or avoid harmful dimensionalresonance which usually exists in a large core. The air gap may befilled with non-magnetic and non-metal material, such as glue or plasticwhich may help to hold different parts together, and such fillingmaterial may be used for cooling of the cores. Some of the windingcores, connection cores and center cores may be integrated to become asingle core assembly. Other arrangement of the coils may also bepossible. For example, they may not be symmetrical or coplanar. As longas they are magnetically coupled through core materials, such couplingcan be used to the advantages of the WPT system design.

FIG. 8B shows another implementation of a coil assembly 800 which issimilar to the one shown in FIG. 8A except that the connection core 806comprises several bars. In the center area 808 there is no core norwinding. As is well understood in the industry, when the coils arearranged symmetrically, and the currents in the windings are alsosymmetrical (i.e. having the same amplitude and frequency, and a phasedisplacement between adjacent windings equal to 360°/N where N is thenumber of coils in the assembly), a rotating magnetic field is generatedabove the coils. In the center region 808 the magnetic field is weak(i.e. has a low flux density) so sensitive circuits such as sensors canbe placed around there.

FIGS. 8A and 8B shows round or circular shape of coils. Other shape ofcoils may also be used. FIG. 8C shows an assembly with triangular coilsto form a rectangular or square charging area. FIG. 8D shows an assemblywith hybrid-shape windings to form a circular charging area, in whicheach winding is in a hybrid shape consisting of part of a triangle andan arc. The coil assemblies shown in FIGS. 8C and 8D operate in similarway to the coil assemblies shown in FIG. 8A except that the windingshape is different, and thus the charging area or space may also have adifferent shape. In a practical system, the winding shape and the numberand location of coils in a coil assembly can be designed according tothe actual needs of the system.

FIGS. 9A and 9B show side views of the coil assemblies shown in FIG. 8.In FIG. 9A, there is a core 902 in each winding 901, and two windings W1and W3 are around winding cores C1 and C3. There is also a center coreC0 903. The coils are coupled through a connection core 906 via air gaps904. The length of the air gap coupled to the center core may bedifferent from other air gaps. In FIG. 9B, each coil is an air-corewinding, and there is no center core. In a practical design, whether touse a core in a coil, whether to have air gaps, and whether to use acenter core are also choices to be decided according to systemrequirements.

The windings in a coil assembly may be interleaved, and may be arrangedinside slots in a magnetic core in a way similar to the stator windingsof a poly-phase axial-flux machine, as is shown in FIGS. 10A and 10B(collectively FIG. 10). Each winding may have the same design with thesame shape and size, all windings in the coil assembly may be arrangedin a symmetrical manner but with a space displacement along theperimeter of the coil assembly. One or both ends of a winding may bebrought out as a connection, and each connection can be coupled to apower converter of a transmitter or a rectifier of a receiver through aresonant capacitor, so a near-sinusoidal current can be fed into itduring operation. The center of the magnetic structure may optionallyhave one or more center cores, and some of these center cores may have awinding around it. Each winding may have multi turns, and the windingsmay also be interleaved as in convention ac motors. FIG. 10A shows threeidentical semi-circular coils arranged with 120° displacement in space.Generally, if there are N coils arranged along a perimeter of the coilassembly, the space displacement among them should be about 360°/N tomaintain a symmetrical arrangement, which helps to generate a smoothrotating magnetic field when currents with the same phase displacementflow in them. Other shapes such as elliptical, rectangular or irregularshapes, can also be used to configure the wingdings, and the number anddisplacement angles may change to better suit a system. FIG. 10B showsthat the three windings of FIG. 10A are placed in a magnetic core 1006,and are interleaved with each other to further enhance the magneticcoupling between these coils. Examples of how the conductors of awinding may be coupled to the core are be shown in FIGS. 12 A and 12B(collectively FIG. 12). FIG. 12 are side views cut through line A-A′ inFIG. 10B. In FIG. 12A, example layouts of windings in a slot is shown,where the windings in a slot may have multiple conductors which belongto one or more windings. Compared to the side view of FIG. 9A, the toothserves as the function of winding core 902, and the base of the coreserves as the function of the connection core 906. In a WPT system, bothRX and TX designs can use this kind of magnetic structure, and the teethmay not have any tip as is shown in FIG. 12A, so the distance betweenadjacent teeth are relatively large, achieving a reasonable magneticcoupling coefficient between a TX coil and a RX coil. The right drawingin FIG. 12A shows that the magnetic material in the tooth part of thecore may be removed, but the windings are still arranged in as if teethwere still there form an air-tooth structure. The air-tooth structureworks similarly to the coil structure shown in FIG. 9B. FIG. 12 B showsthat multiple conductors or windings may be arranged in a top-bottommanner or a side-by-side manner, using air-tooth structure as anexample.

When a RX magnetic structure is placed in proximation of a TX coil,magnetic coupling between RX coils and TX coils are established soenergy can be transferred between them. The distance between the RX andTX magnetic structures can vary in a wide range, from a few mm tohundreds of mm. With the coil assembly discussed above, the magneticfield around the magnetic structure now is formed collectively by thewindings/coils in the structure, and the number of coils may have littleeffect on the magnetic field in the charging space around the magneticstructure directly. In this way, the number, shape and size of RX coilsmay be different from the number of TX coils in a system, giving morefreedom to the system design, especially when a transmitter is used towork with different receivers with different power levels in differentsystems, which is usually required in many applications such asautomotive charging stations. Also, during an operation mode, some TX orRX resonators may be deactivated (i.e. the current in the associatedcoil is very low or zero), and the number of active TX coils (i.e. TXcoils flowing with current to contribute to the magnetic field betweenthe RX and TX coils) may be different from active RX coils. When a RXmagnetic structure is placed in a nearby region facing a TX, itswindings will generate voltages and/or currents through induction. Also,as the frequency of winding currents are usually high, significant powerand/or energy can be transferred from TXs to RXs or vice versa over arelatively long distance at a good efficiency. When there is a failurein a winding or its associated converter, or when a module is shut downintentionally in light load to reduce power losses, the number of activemodules in the system, including the number of active power convertersand active coils in a coil assembly may be reduced. The phasedisplacement among the currents of coils in a coil assembly may beadjusted to generate a rotating magnetic field. The flux distribution inthe charging area may no longer be even or symmetric, but the system cancontinue to operate and the remaining windings and converters can stilltransfer power and energy to the output. This can significantly increasethe reliability and light-load efficiency of the WPT system.

The conductors in a slot may belong to the same winding or differentwindings. FIG. 11 shows a winding arrangement to achieve multiple turnsin a winding in a structure with 12 slots. Each slot has two or moregroups of conductors, and each group may have multiple turns from onewinding. Each winding has a positive segment and a negative segment. InFIG. 11 each slot contains two groups, and in some slots the two groupsof conductors may be from one winding, and in some other slots the twogroups may be from two different windings. The groups may be be put sideby side, or one on top of the other in a slot. In FIG. 11, 3 windings(A, B, and C) are formed, winding A with A+ and A− as positive andnegative segments, winding B with B+ and B− as positive and negativesegments, and winding C with C+ and C− as positive and negativesegments. One side of the leads, A+, B+, and C−, or A−, B−, and C−, maybe connected together as a center point, or both ends of each windingmay be brought out as connections to be coupled to power converters andresonant capacitors. Similar arrangements may be made to have more orfewer windings, and some windings may be put into series or parallel. Inthis way, the windings are arranged in similar techniques as inpoly-phase ac electrical motors, and all winding and core technologiesfor such motors can be utilized to make coils for a WPT system. However,as each winding in a WPT system is coupled with a resonant capacitor andoperates close to resonant mode, the winding current is naturally closeto a sinusoidal waveform. In FIG. 11, each winding starts and ends witha partial slot, and a smooth rotating magnetic field with low spaceharmonics can be established in a space above the magnetic structurewhen sinusoidal currents with symmetrical phase shifts (phasedisplacement) are fed into the windings.

Although coplanar and symmetrical arrangements of windings areillustrated in the examples, the arrangement of windings and/or coilsmay not need to be coplanar nor symmetrical. The shape of a TX or RXmagnetic structure may be arranged in any shapes, such as circular,rectangular, or irregular shapes.

FIG. 13 shows a system with a TX coil assembly and a RX coil assemblyplaced in proximity, and with the magnetic coupling between TX coils andRX coils established. A transmitter (TX) coil assembly 1305 may havemultiple coils 1301 placed around a TX core 1304, which may include aconnection core and a plurality of winding cores as discussed earlier. Areceiver (RX) coil assembly 1310 may have multiple coils 1306 placedaround a RX core 1309, which may include a connection core and aplurality of winding cores as discussed earlier. The number oftransmitter coils may be different from the number of receiver coils.When a RX coil assembly (or RX) gets close to a TX coil assembly (orTX), each RX coil will be in magnetic coupling with each TX coil, butthe strength of the coupling between a particular TX and a particular RXcoils changes as the relative position of the RX and the TX changes. Bymeasuring the relative strength of the magnetic coupling betweendifferent TX and RX coils, the relative position of RX and TX can beobserved and sensed, and this information can be used to guide the RX orthe TX into the best charging position if the RX or the TX is movable.Please note that the magnetic coupling strength may not need to bemeasured directly. For example, measuring a voltage signal across awinding or a circuit coupled to a winding may be a better option. When aTX senses a RX is getting into the charging area, it can send a currentwith a suitable magnitude and frequency to each transmitter coilsequentially, and the RX can measure a signal associated with a voltageor current in each RX coil which is related to and serve as an indicatorof the magnetic strength in the RX core in the coil, to get anindication signal of the magnetic coupling coefficient or magneticcoupling strength through the received RX signal amplitude. In a systemwith N transmitter coils and K receiver coils, the coupling coefficientdata can form a K×N or N×K matrix. By analyzing this coupling matrix,the relative position and angle of TX and RX can be obtained. Artificialintelligence (AI) and machine leaning algorithms can be used toincorporate large amount of simulation data and testing data, includinghistorical data, in this process to get more accurate information.

As the wireless power transfer depends on magnetic induction, a metalobject in the charging area can present dangers of over-heating and mayinterfere with the power transfer. Foreign-object detection may be usedto protect a WPT system. A good way to do this is through using propersensors. The sensor may be placed in the TX or RX. If a metal is in thecharging area, the magnetic field in the area will cause significantinductance change or power loss and/or temperature change in the metalobject. By sensing the temperature change or relative temperature in thecharging area, potential danger and/or operational interference may bedetected. A way is to use an arrayed infrared (IR) sensor with widesensing angle to monitor the temperature of the charging area, andidentify the location of metal object(s). AI and machine learning can beused to process the IR imaging data, incorporating testing, simulationand operation data in the process. Another way to detect a metal objectin the charging area is to analyze the coupling matrix. Due to thesymmetric arrangement of the coils in the RX and TX, irregularity in theelements of the coupling matrix may also indicate a metal subject in thecorresponding area. When a metal object or potential danger is detected,the whole WPT system, or just the affected TX module(s), can be shutdown for protection, or can work in a reduced power mode to avoidover-heating danger of the metal project. FIG. 13 shows that a sensor1307 may be put in the center region of the RX, and/or a TX sensor 1302may be put in the center region of the TX, where the flux density in thecenter region of a coil assembly can be arranged to be low so thesensors can operate reliably. Such sensors may be used for metal objectsensing or other purposes. Of course, more than one sensors can be usedin a TX or RX, or there may be no sensor in a TX or RX.

A limiting factor in a WPT system is the stray magnetic field outsidethe charging area. With the modular design of resonators describedabove, the magnetic field tends to concentrate around the space adjacentto the RX and TX coils, and the strength of stray magnetic field outsidesuch charging space can be much reduced. A magnetic shield can beemployed to further reduce the stray magnetic field. FIGS. 14A and 14B(collectively FIG. 14) show examples of using magnetic shielding. InFIG. 14A, a cylinder shield 1403 may be placed around the RX and RX, andthe cylinder may have multi layers (two layers shown as an example): onelayer of magnetic material 1404 which has high magnetic permeability,and one layer of metallic material 1405 which has high electricconductivity. The shield may use also materials like silicon steel whichcan conduct both electrical current and magnetic flux. With such anenclosed shield, the stray magnetic field outside the charging area canbe reduced significantly. However, a shield doesn't need to cover thewhole charging area or form an enclosed shape. A shield may be placed toprotect just sensitive areas as is shown in FIG. 14B. FIG. 14B shows anexample with two localized shields 1403. A shield may be just a siliconsteel or Aluminum sheet separating the charging area and a sensitivearea, which may be a place where electronic equipment is located orhuman being may enter during a WPT system's operation.

In case some modules are shut down during low power operation, theselection of active modules may consider their effect on stray magneticfield in the sensitive area and maintain a more or less symmetricoperation. For example, in FIG. 14B, if two modules are to be shut down(or de-activated), module 1 (associated with coil L1) and module 3(associated with coil L3) may be shutdown, so Coil 2 and Coil 4 arestill active. Coil L2 and coil L4 now may be controlled to conductcurrents with opposite polarity based on the symmetrical principle, sothe magnetic fields they generate tend to cancel each other out in thesensitive areas A and B, so the strength of stray magnetic field is muchreduced in these areas.

Each coil may be coupled to a dedicated power converter (a TX converteror a RX rectifier) in a modular WPT system, as shown in FIGS. 2 and 3.However, multiple power converters may be integrated into a multi-phaseconverter, as will be demonstrated in FIGS. 15 and 16. FIGS. 15A and 15B(collectively FIG. 15) show two examples of implementing a multi-phaseconverter. In FIG. 15A, there are 3 resonators 1503, each consisting ofa resonant capacitor Ct and a coil Lt, and 3 power converters 1501. Eachpower converter 1501 operates as a phase of the multi-phase converter1508. A resonant capacitor can be implemented as a switchable orvariable capacitor. The coils may be magnetically coupled together toform a coil assembly 1507, and one end of the associated windings may becoupled together (to a center point). If the windings are designed andarranged symmetrically and controlled symmetrically, the sum of allwinding currents in a TX or RX should be zero or close to zero in steadystate operation in average sense. The center point can be left floating,or be coupled to a point with stable voltage. In FIG. 15A, the centerpoint is connected to a voltage-split circuit 1502 consisting of twocapacitors C1 and C2 in series. One of C1 and C2 may be omitted withoutimpacting the steady-state operation. The center point can also beconnected to the negative or positive terminal of the dc voltage (Vo orVdc) through an impedance circuit such as an inductor and/or acapacitor, and a switching network such as a half-bridge converter. Thepower converters may be all half-bridge converters. Of course, moreconverters, or converters in other topologies may also be used. FIG. 15Bshows a system having N full-bridge power converters 1501 and Nresonators 1503, each consisting of a resonant capacitor Ct and a coilLt. The N coils may be magnetically coupled together to form a coilassembly 1507. Both ends of a resonator are connected a full-bridgeconverter. The transmitter 1500 in FIG. 15 is controlled by atransmitter control system 1504.

Multi-phase receivers can be implemented similarly as the multi-phasetransmitter disclosed in FIG. 15. FIG. 16 show an example three-phaserectifier system with 3 receiver resonators 1603, three half-bridgerectifiers 1601, and a voltage split circuit 1602 consisting twocapacitors C1 and C2. The voltage split circuit is an impedance circuitand may be replaced by other impedance circuits. Diodes are used in therectifiers, but active switches such as IGBTs and MOSFETs can also beused as synchronous rectifiers as is well known in the industry. Eachresonator consists of a resonant capacitor Cr and a coil Lr. Theresonant capacitor may be implemented as a switchable or variablecapacitor. The coils may be magnetically coupled together to form a coilassembly 1607, and one end of the associated windings may be coupledtogether (to a center point). If the windings of the coils are designedand arranged symmetrically and controlled symmetrically, the sum of allwinding currents in the RX should be zero or close to zero in steadystate operation in average sense. The center point can be left floating,or be coupled to a point with stable voltage. The center point can becoupled to a voltage-split circuit consisting of C1 and C2. In steadystate operation, the center point is then at ½ of the dc link voltageVdc. One of C1 and C2 may be omitted without impacting the steady-stateoperation. The center point can also be connected to the negative orpositive terminal of the dc voltage (Vo or Vdc) through an impedancecircuit such as an inductor and a switching network such as ahalf-bridge rectifier. The receiver 1600 is controlled by a RX controlsystem 1604, which may include controlling the output voltage, power orcurrent of the receiver by adjusting the capacitance of a resonantcapacitor or each resonant capacitor.

By changing the capacitance of a resonant capacitor the current in aresonator may also be changed, which can be used to achieve current orthermal balance between the different resonators, coils, modules, powerconverters and/or rectifiers. By setting the capacitance of a resonantcapacitor in the TX and/or RX resonator to its minimum value, aresonator may be also put into an idle mode.

As the magnetic field in the charging space are generated by multipleresonators collectively, the resonators and power converters may also becontrolled collectively. In steady-state operation, the winding currents(coil currents) in a multi-coil TX system should be controlled with asymmetrical phase shift among the phases, and the current amplitude ineach active transmitter coil may be controlled to be the same to form abalanced multi-phase system. Since the coils are distributed in spaceevenly with symmetric space angles, the current in each coil should havethe same phase angle as space angle of the coil. This will result in asmoothly and evenly rotating magnetic field in the charging space.However, Due to the possible dis-alignment between the RX and the TX ina system, the TX resonant capacitor in the resonator of the RX and/orthe TX may be configured to be different from that of another resonatorto achieve such balance. The power switches in a transmitter may beswitched at 50% duty cycle so soft switching (zero-voltage switching orzero current switching) of the switches can be achieved to reduce powerlosses and noise in the system. Alternatively, the power switches may becontrolled in a phase-shift manner to achieve soft-switching operation.50% duty cycle control and phase-shift control for multi-phaseconverters are well known in the industry. In transients, the duty cycleof switches may also be adjusted, and the top switch and bottom switchin a phase leg can be switched on and off in a complementary orsymmetrical manner. The switching frequency and duty cycle of switchesmay be used for power control, and also be controlled to keepsoft-switching of the power switches or to fulfil other systemfunctions. For example, the duty cycle may be increased gradually in astart-up process to achieve soft start. Each of the resonant capacitorsmay be implemented as a switchable capacitor or variable capacitor. Theresonant capacitance in a TX module may be adjusted for power control orfor soft-switching of power switches in the module. The resonantcapacitance adjustment in a RX module may be adjusted for power controlor for soft-switching of power switches in the module. The capacitanceadjustment of a resonant capacitor can also be used for faultprotection, voltage limiting or circuit isolation, as a low capacitancemeans a high impedance to limit current through it. As the circuits fora receiver and a transmitter are symmetrical, the role of RX and TX in asystem may be interchanged. For example, a receiver with synchronousrectifiers may be controlled to operate as a transmitter. This alsoallows a WPT system be bidirectional in power delivery. Again, most ofthe circuit can be shared with a wired charging system with similarmethods as shown in FIGS. 4 through 6.

During light load, the number of active TX modules may be reduced toincrease system efficiency. Symmetry may be kept during a reduced-moduleoperation with the phase displacement between winding currents adjustedaccording to the actual number of modules. For example, a six-modulesystem can be first reduced to a 3-module system, a two-module systemand a 1-module system while still keeping a symmetrical configuration.

The spectrum available for wireless charging is limited by world-wideEMC regulations. Currently, several example frequency bands may beconsidered for WPT: 6.78 MHz, 100-148 kHz, 81-90 kHz, 60 kHz and 20 kHz.For a high power application, the control system may use more than onebands for power control to fully utilize the spectrum resources.Multi-band frequency control and capacitance switching can be combinedin power control to provide a wide power range while keeping theswitching frequency in the allowed WPT bands. Number of modules can alsobe used in power control. Usually, a system has both active power andreactive power. The active power is related to power delivered to theoutput, and controlling the active power can control the output power,output voltage or output current. The reactive power is related to thesoft switching of power switches in the power converters. A good controlstrategy should consider both the active power control and reactivepower control. In a resonant power conversion such as the resonatorsused in WPT systems, both reactive power and active power are dependenton the switching frequency, the inductance of the coil, and thecapacitance of the resonant capacitance. So it is feasible to use anycombination of these variables for active or reactive power control.Usually, it is difficult or expensive to control the inductance of acoil dynamically, and thus we will use the combination of frequencycontrol and resonant capacitance switching as an example to explain thecontrol of a WPT system. In such a system, a WPT system may have threeindependent control variables: the switching frequency, a TX resonantcapacitance, and a RX resonant capacitance. Any of these variables canbe used to control the active power or reactive power, and thereforethere are freedom in setup the best control strategy for a particularapplication, in order to reach a system with the right active power toregulate the output to the desired voltage/current/power at the systemoutput, while keeping the reactive power at the power converter outputwithin a low and inductive range so the switches in the power converterscan have soft switching (particularly zero voltage switching). For highpower applications, in normal operation it may also be desirable toadjust the RX resonant capacitance so that the resonant frequency in theRX resonator is the same as or close to the switching frequency, inorder to minimize the currents in TX coils to improve the efficiency ofthe system. An example control strategy may include:

-   -   1. For frequency bands with a wide range of frequencies (such as        100-148 kHz or 81-90 kHz), the switching frequency can be used        as the main control parameter, and if needed resonant        capacitance may be used as a secondary control parameter. When        the switching frequency reaches the higher or lower limit of the        band, a resonant capacitor can be switched to the next value to        bring the frequency back to the range. When the highest        capacitance or lowest capacitance is reached, then the switching        frequency may be hopped to an adjacent band if needed.    -   2. For frequency bands with a narrow range (such as 6.78 MHz, 60        kHz or 20 kHz), resonant capacitance may be used as the main        control parameter. When a switchable capacitor with        predetermined capacitance values is used as a resonant        capacitor, the resonator may be controlled to switch or jump        between two adjacent values of the resonant capacitor regularly        or irregularly, for example in a PWM manner where the relative        time (duty cycle) of the resonator operating with a capacitance        value may be used as a power control means or a hysteresis        manner where whenever the output reaches a limit the capacitor        is switched to the other capacitance value. When the capacitance        of the resonant capacitor reaches to its limit, the switching        frequency may be hopped to an adjacent band.    -   3. A TX may be controlled to regularly hop from one frequency        band to another (or to a shutdown mode with zero output power)        with a suitable frequency, usually in the range from a few        hundreds to a few kilo Hz. The relative time (duty cycle) of a        TX operating in a band may be used as a power control in this        hopping mode. The advantage of this control compared to        conventional burst control where the power switches may not be        switched for some duration of time is that the power switches        are always switching, so the system is capable of transferring        some energy all the time, thus small devices such as sensors may        be powered by the energy in the magnetic field.    -   4. The resonant capacitance in a TX module and the resonant        capacitance in a RX module may be used simultaneously for power        control, and the control in RX and TX may be coordinated through        a communication system.    -   5. The duty cycle of the transmitter power converter may also be        used as a control means under light load conditions. As the duty        cycle control in a multi-phase converter may also achieve soft        switching of the power switches with phase-shift control or        complementary control of top and bottom switches in a phase leg,        the power loss and noise level in the system may still be low,        but the winding currents and thus the resulting in magnetic        fields may have stronger contents at even-order harmonic        frequencies. However, if the winding current is relatively low,        the EMI effect of the even-order harmonic currents may still be        manageable.

For example, a WPT system for an electric vehicle application may bedesigned to work within 81 kHz to 90 kHz range in normal operation. Itmay use the switching frequency Fsw as the main control parameter. Forexample, when the output power (voltage or current) is higher than itsreference value, the Fsw is reduced to decrease the power output, andwhen the output power is lower than its reference value, the Fsw isincreased to increase the output power. After the Fsw reaches the highlimit FswH (90 kHz in this case), the resonant capacitance in TX or RXis switched to the next higher value, and Fsw and duty cycle of thepower converters may be coordinated with the capacitance switching toachieve a smooth transition. After capacitance reaches the high limit,if the delivered power is still lower than the requirements, the numberof active modules may be increased. If all modules are already inoperation and the control system still asks for more power, the WPTsystem has reached its highest power capability in this frequency band,and cannot support higher power demand in this band. The system caneither go to a higher frequency band or reduce the output powerrequirement to maintain a smooth system operation. After Fsw reaches thelow frequency limit FswL (81 kHz in this case), the resonant capacitancein TX or RX may be switched to next lower value, and Fsw and duty cycleof the power converters may be coordinated with the capacitanceswitching to achieve a smooth transition. After the lowest capacitanceis used, the number of active modules may be decreased. If the number ofmodules is reduced to its minimum and the output power is still higherthan required, the WPT system has reached its lowest output power withinthis band, and should go to next lower frequency band, 60 kHz forexample. Duty cycle and/or resonant capacitance can be changed duringthis band hopping process to limit the current and voltage stresses inthe system to obtain a smooth transition. At 60 kHz band, the systemcannot use switching frequency as the main control parameter. It can usethe resonant capacitance, input voltage to the power converter or switchduty cycle as the main control parameter. The power converter may workin burst mode to reduce the output power further, or go to a lowerfrequency band, 20 kHz in this case, to reduce power. The number ofmodules can be used to manage power output and to reduce power lossesduring light load operation.

FIG. 17 shows an example control flow chart in a wide frequency band,and FIG. 18 shows an example control flow chart in a narrow frequencyband. These figures just show the basic logic, and many variants can bemade in implementation.

The power control can be made at a module level, or at the system levelto treat the system as a single multi-phase system, with a module as aphase. Please note that the number of phases in a TX may be differentfrom that in a RX.

This disclosure has given examples to illustrate the invention. Theremay be different variants in implementation. For example, seriesresonant tanks are used in the figures as examples. Parallel resonant,series-parallel resonant, parallel-series resonant and multi-branchresonant can all be used, with frequency and capacitance controladjusted accordingly.

Although embodiments of the present invention and its advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the invention as defined by the appended claims.

Although embodiments of the present invention and its advantages havebeen described regarding to mainly WPT systems, the technologies can beused in other power conversion systems such as power converters, powersupplies, and wired charging equipment.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. A device comprising: a plurality of coilsarranged along a perimeter within the device, wherein each coilcomprises a winding configured to be coupled to a power converterthrough a resonant capacitor, each coil forming a resonator with theresonant capacitor; a connection core magnetically coupled to theplurality of coils; and a plurality of power converters, wherein eachpower converter is coupled to one of the plurality of coils andconfigured such that a current flowing through the winding of the coilhas the same frequency as other winding currents in the device, and thephase angle of the current is approximately equal to the space angle ofthe coil, so a rotating magnetic field is formed in a space around thedevice.
 2. The device of claim 1, wherein the device is a transmitter ora receiver of a wireless power transfer system.
 3. The device of claim1, wherein the plurality of power converters forms a multi-phase powerconverter.
 4. The device of claim 1, wherein the windings are placedclose to the connection core and interleaved to further improve themagnetic coupling between the windings.
 5. The device of claim 1,wherein a resonant capacitor is a switchable capacitor or a variablecapacitor.
 6. The device of claim 5, wherein the capacitance of theresonant capacitor is controlled to balance the currents in thewindings.
 7. The device of claim 5, wherein the capacitance of theresonant capacitor is adjusted to control a voltage or a current of thedevice, or to protect the device.
 8. The device of claim 1, wherein somecoils are de-activated during a mode of operation, and wherein the phaseangles of winding currents are adjusted according to the number ofactive coils.
 9. The device of claim 1, wherein the switching frequencyof the power converters is adjusted or hopped.
 10. The device of claim1, wherein the resonators are coupled to a wired charging connectionblock, and wherein the resonators and the wired charging block areconfigured to operate the device in either a wired charging mode or awireless charging mode.
 11. A system comprising: an input port having aninput voltage; a first power converter coupled to the input port andcomprising a first switch network having a plurality of first powerswitches; an output port having an output voltage and an output current;a second power converter coupled to the output port and comprising asecond switch network having a plurality of second power devices; aresonator block comprising a plurality of resonators, wherein eachresonator comprises a resonant capacitor, and wherein a first resonatorof the plurality of resonators is coupled to the first power converter,and a second resonator of the plurality of resonators is coupled to thesecond power converter; and a connection block comprising a switchingdevice and coupled to the first resonator, wherein the connection block,the first resonator and the second resonator are configured such thatthe system operates in a wireless charging mode with the resonator blockactivated or a wired charging mode with the connection block activated.12. The system of claim 11, wherein the first resonator or the secondresonator comprises a plurality of coils distributed symmetrically inspace and magnetically coupled to a connection core, and each coil iscoupled to a resonant capacitor, and wherein the currents in the coilsare controlled to generate a rotating magnetic field in a space adjacentto the coils.
 13. The system of claim 11, wherein the capacitance of aresonant capacitor is adjusted to deactivate the resonator block.
 14. Amethod comprising: configuring an output port of a system to have anoutput voltage and output current; providing a plurality of firstresonators, wherein each first resonator comprises a first resonantcapacitor and a first coil, and wherein the first coils are placed alonga first perimeter, and through the first resonant capacitors the firstcoils are connected to a plurality of first power converters comprisinga plurality of first power switches; providing a plurality of secondresonators, wherein each second resonator comprises a second resonantcapacitor and a second coil, and wherein the second coils are placedalong a second perimeter, and through the second resonant capacitors thesecond coils are coupled to a plurality of second power converterscomprising a plurality of second power switches; establishing a magneticcoupling between the first coils and the second coils; and configuring acontrol block to control the system such that a rotating magnetic fieldis established between the first coils and second coils in a mode ofoperation.
 15. The method of claim 14, further comprising controlling atleast two variables selected from the switching frequency of the firstpower converter, the capacitance of a resonant capacitor in the firstresonator, and the capacitance of a resonant capacitor in the secondresonator to regulate the voltage or current at the output port whilemaintaining a soft-switching of a first power switch.
 16. The method ofclaim 14, wherein the number of active first coils is different from thenumber of active second coils in a mode of operation.
 17. The method ofclaim 14, wherein the first coils are magnetically coupled to each otherthrough a connection core.
 18. The method of claim 14, furthercomprising configuring the control block such that the capacitance of aresonant capacitor switches between two predetermined values in a modeof operation.
 19. The method of claim 14, further comprising sensing amagnetic coupling strength signal between each first coil and eachsecond coil, and using the magnetic coupling strength information toguide the moving of the first coils or second coils so a better magneticcoupling is established between the first coils and the second coils.20. The method of claim 14, further comprising sensing a magneticcoupling strength signal between each first coil and each second coil,and using the magnetic coupling strength information to detect a metalobject in the space between the first coils and the second coils.